Prevention of hydrogen blistering and fissuring



Feb; 5, 1957 "r. SKEI ETAL PREVENTION OF HYDROGEN BLISTERING AND FISSURING 4 Sheets-She et 2 Filed Oct. 25, 1954' CYANIDE Mama 8 6 1oz. 523w uwn 3 J58,

DAYS 40C DAYS @4-QC FIGURE 1!.

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PREVENTION OF HYDROGEN BLISTERING AND FISSURING Filed Oct. 25, 1954 4 Sheets-Sheet s fieuaelfi.

\nvnfor'; 'Thursfon Ska] Wiih'a A.Bonnr Thzir'Agz 1' Feb. 5, 1957 T. SKEI EIAL PREVENTION OF HYDROGEN BLISTEERING AND FISSURING H 1 l a. n m .m S H 0; N

s o A I a zorc om 6 TE 9 M .1 m W m w s w H u 4. 5 m m 5 2 t c o d e 1 1 F THEIR AG ENT United States Patent 6) Thisinvention. relates: to the prevention. of.- hydrogen li t r ng sand fissuring. he prevention: ofi hydrogentdamagejnequipment utilized 1 .16 production handling-.andtreatment; ofipetroleum; 1d:'frae.t inmsi; thereofi Additionally, it :relates to methods ;of 1operating unitszutili'zed: in such production,

handling :andxgtreating operations so as .to minimize. or: COmfilQIflKfiHmllifltQ the-problems associated ;with ablistereing; and fissuringiof the equipment utilized therefor Th e tpmb msuare :closelymelated: to, and often a re.- sult of, phenomenon knownras. hydrogen penetration,

'lih is; aphenornenon is believedrtm betprincipally one Kain-fvolving difiusiongtQxthe lmetal :o.;-atomic hydrogen; The.

usual efteet of; pcnetration Lof atomic,hydrogemintosteela or other ferruginous metals is; armarked' changejnrthei physicahproperties .of; the :steel :such tha t; the :steeh becomes very; brittle. particular? phenomenon. ist know-n in.

th artas; hydrogenembrittlernent.

Under manyqcircumstances ofrhydrogen: embrittlemenn. iiathe conditions lead ngto penetrationi of atomic 1 hydro-z gen into the, :steel are removed, the atomic =hydrogenswi-llhe; released ;fromi-;the meta1, and the A properties; of: the steel; will: return to; normal: Under other: circumstances, however, the; atomic hydrogen; may, combine with; the. metal tot-form; molecular-hydrogen; whiehnis': unableittot f rt er h 'ou hrt etme t; fisu fi ienttmol eulan yd oge or 'sny Po nt, lar e pre ures: maythe; builtup. within the metal, causing into-rip orrtear around;

thistpoint of pressure build-up At. least oneofithedaetors influencing .the-formation of mole ydr en fr m t mie y rog n. hfQK-P Q fi 0 l is cn inaitiesm r u a ie nz he wmposuona of the steel These.,;m ay result frorn irnpurities,suchzas; slag inclusions-, small voids-caused by. trapped gasesz-iandathe like. Even the (st ess resulting from thermal treat mentaor cold working may give lsuflicientt irregularity inthe metal so; as; to promote formation. of molecular hydrogen,

The result of the rupture of themetal by themoleculaig; hydrogen pressure is usually observed on the metalasur face asblister-like. raised;v portions I or as open g-fissures. This physical;stressing and. rupturing observed -as;bliste,r-

ing;.and or. fissuring wil-ljhe referred tov hereinafter ast d n m e= The; pene tration. ofjatomiczhydrogen into steel has been-.3 widely studied; lt isafairlyywell :established. that forv the]: hydrogentodifiuseinto thelmetal two conditions mustlhe simultaneously met: There .must be. maintained on the.

surface of the-steeL-a highnconcentration Of-fltOlIliQhYdIOw:

genand; the surfaceof the steel must activelypromote. the acceptance of atomicghydrogentrather than catalyze the...

More specifically, it-.:relates; to;

2,780,583 Eiatented Feb. 5 1957 associationof atoms atoamolecules of h'ydrogen." Withrespect tor the .firstxconditiongit has-beenfound that-rninuteamquntsaof atomic=hydrogen will yield "(by diffusion" intothe; metal ands combination: to molecular: hydrogen);-

enough molecularthydrogenrto cause very seriousblister ing .and/or fissuringi. Thus, there -cambe-and= often. -is

extensive hydrogentdamage with only-a negligibleamounfi oftcorrosion damagea Hydrogen damage occurs particularly in the petroleum; industry; in r equipment: contacted by sour erodes, sour natural-:gases and agasolines; and like products which areknown ltd containiappreciable:- quantities ofhydrogem sulfides. When hydrogmblistering hasbeen serious; a-- certain reduction therein: mayabeeffected by partial neutr alizationtof hydrogencsulfide: witha basic: constituent such as gaseousrammonias However; in instances where very. largequantities .lofahydrogen sulfide-were present"; the 1' injectioniofi ammonia; did :nqtualways alleviate the hydro genada'mages Imfact; in many. instances injection -of an 1fmonianhas; actuallyuincreasedtthe difficulty. Moreover;

the injection of large amounts of ammonia causes other" difliculties, suchtasaplugginglofzequipment bydeposib'of inorganic'saltsesuehvast-ammonium; carbonate. The in dust-try *has sufieredrgreat: losses .-by .hydrogen damagedue bothto.replacementrequirementsof equipment which has been :extensivelysdamaged :and to operating, time l'o'st -due to shut:dtmznsrsfori,repairs and :inspections of equipment. The normah overhead .vaporL-stream from certainre fin'cry operationsmay contaiirin addition to hydrocarbons and hydrogen tsulfideaappreciable amounts of hydr'ogen, CQIbOIILdiOXidLCHIb6IL monoxide; water and-ammonia.

Hydrogen .cyanideioftemis present; particularlyin streams-'- following; aucracking operationr lrilattemptingrto identify thetcauses of hydro gen-damage the.effectmfzrsome:.ofrthe components already listed: were. investigated-uinitheefollowingamanner: A hollow: steel F capsule..ivas; -innnersediniaqueonssolutions of the compoundsiinvestigateds Thelinsidenofztthe capsule was connestedtojagasanetenbymeans Of a capillary tubing.- I1

theasolution:swereeanaactivespromoter" of hydrogen pene tration atomic hydrogen .wouldditfusesthrough the metal 1 and scomhine;as;.1noleculars hydrogennonthe, inside of' the' capsule. Theavolumeaof: hydrogen. which difiused into thegcapsule was recordedaby-theemeter andzwasa measure of:theyactivityz.of thesolution. The solutions were main tained between ambient room temperature=and-40 C. during ;alla.'tests..1 Hydrogen-a penetration in-yt'ne absence of:hydro gen sulfidqiwasscompletelyabsent for all practical-purposes. shownzgraphicallyvin Figt; IA D-.

As can; beseen-fromrfigure IAywhen; an aqueous solutiontwas saturated With:hydrtogenxtsulfide a high initial rate 05' hydrogen.penetrationswas observed, The addition .of1.moderate. .amounts of ammonia toa saturatedhy-* droge: sulfide solution essentially prevented hydrogen-penetration, as shown-ilr FigureglBi However by the addi tion of cyanide ions (see-Figure"IC)*-it was' found that afteran initial period of -low activity; hydrogen penetration commenced andremained-ataahigh level: Similarly," addition of moreammonia- 1o the solution (as indicated in -Figure ID-) containing moderate amounts of ammonia also: resulted :in development -of ahighly active medium for penetration-of;hydrogen. I

The exact-phenomena involved-"in causing hydrogen=- penetration under these conditionsehave not been; eluci- Results of somesof; the investigations are 3 dated. However, it appears that the primary reaction for production of hydrogen may be represented by the following equation:

The solid iron sulfide formed frequently stifles further reaction unless removed from the steeel surface. Thus in the presence of cyanide ion the iron sulfide is dissolved as ferrocyanide and the hydrogen-producing reaction continues unabated. When large amounts of ammonia and hydrogen sulfide are present the corrosion product does not adhere to the metal surface and again the hydrogenproducing reaction continues unabated. This reaction is particularly prevalent at high pH values (above about 8.0) at a hydrogen sulfide partial pressure of 15 p. s. i. a. This reaction also occurs at lower pH values when the hydrogen sulfide pressure is increased to several atmospheres.

While the above theories are believed to be supported by fact, the present invention is not to be restricted to the validity of the theories, since the result of the treatment to be described hereinafter has been found to substantially inhibit hydrogen penetration.

It is an object of the present invention to substantially inhibit hydrogen blistering. It is a further object of the present invention to treat hydrocarbon streams containing aqueous dispersions of hydrogen sulfide so as to substantially reduce or inhibit hydrogen damage. Other objects will become apparent from the description of the invention.

Now, in accordance with the present invention, it has been foundthat hydrogen blistering of ferruginous metallic containers by hdrocarbon mixtures contaminated with atomic hydrogen-producing compounds and water may be substantially inhibited or prevented by maintaining said mixtures at a pH above about 7 and also maintaining therein a small amount sufficient to substantially prevent hydrogen blistering of an inorganic polysulfide which is soluble in the aqueous phase present in the system.

Still in accordance with this invention a preferred method for minimizing hydrogen blistering comprises the injection of an inorganic oxidizing agent (preferably an oxygen-containing gas) into a system containing hydrogen sulfide and an aqueous alkaline medium whereby a portion of the sulfide is oxidized to produce sulfur, the sulfur thereupon being dissolved in the aqueous alkaline sulfide medium to form polysulfides, which in turn have been found to substantially inhibit atomic hydrogen penetration. Suitable oxidizing agents which may be used in addition to or in place of oxygen include halogens (chlorine, iodine, bromine), chromates such as potassium or ammonium chromates, chlorates such as sodium or lithium chlorate, nitrites such as sodium or potassium nitrites, alkali metal sulfites, ferric salts, sulfur dioxide, and vanadic acid.

Alternatively, of course, a preformed water-soluble polysulfide may be injected into such systems, such as an aqueous solution of an amonium or an alkali metal polysulfide. A representative polysulfide solution which has been found to be effective can be made as follows: hydrated sodium sulfide (387 pts. by wt.) and sodium hydroxide (40 pts. by wt.) are dissolved in water (1000 pts. by wt.) to which sulfur (96 pts. by wt.) is added to form an aqueous solution which is about 1 molar in sodium hydroxide and about 1.5 molar in NazSa. Alternatively, one can utilize spent caustic solutions obtained from I-I2S removal from gas streams and which are available as waste products at most petroleum refineries. Elemental sulfur can be dissolved in typical spent caustic solutions at the rate of about 107 g. of sulfur per liter of spent caustic to form a polysulfide solution which ishighly effec tive for introduction into the subject systems, effecting the substantial reduction of hydrogen blistering.

It is postulated that polysulfide reacts with the primary corrosion product R8 to give a compound FeeS (wherein x is a variable integer of 1 or more and y is an integer of 2 or more) that adheres to the steel surface and prevents further reaction:

While the above theorized reaction of polysulfide ions in the substantial inhibition of hydrogen penetration has not been fully established, it has been found that when water soluble inorganic polysulfides are present in the aqueous phase and when the alkalinity of said phase is between pH of about 7 and about 10 (and preferably between pH 8 and about pH 9), hydrogen blistering is reduced to a minimum, particularly as long as a concentration of polysulfide in the order of at least about 0.1 g. per liter (expressed as free S of aqueous phase) is maintained at all times. Preferably the ammonium polysulfide is maintained between about 0.2 and 1 g. per liter of aqueous phase, although proportions in the order of between about 0.010.5% may be useful under the varying circumstances encountered throughout the wide variety of systems to which the present invention may be applied. The unexpected effect of maintaining close control of the pH utilized in conjunction with polysulfide addition to gas recovery systems and the like is emphasized by the data presented in Figure IV. The effect of pH on the hydrogen penetration rate observed under various conditions is shown in this figure. It will be seen that in the absence of air or polysulfide a minimum hydrogen penetration rate existed in the range between about pH 7.3 and 7.8. However, when air was injected with the consequent formation of excess polysulfide, the rate of hydrogen penetration essentially vanished for all pHs above about 7.8. Hence, the lower limit of pH for negligible hydrogen penetration is definitely set at this figure in gas recovery systems where air or polysulfide is present. Itis important to emphasize that the minimum pH range is entirely different from the tolerable pH range wherein air or polysulfide is not being utilized.

While this sets the lower limit at ph 7.8, the upper limit is imposed by the deposition of by-product salts in operating equipment. At a number of locations in the normal gas recovery plant, ammonia or a base is used to maintain the desired pH. Under some operating conditions, the ammonia requirements may be relatively high. As a result, ammonium bicarbonate may be deposited in tubular equipment and lines. Both ammonium bicarbonate and ammonium carbonate monohydrate have been identified by X-ray diffraction in such deposits. Ammonium bicarbonate deposition increases with the partial pressure of carbon dioxide, the parital pressure of hydrogen sulfide and pH. On the other hand, solubility increases with temperature. A small change in pH has a relatively large effect on ammonium bicarbonate deposition. This is fortunate, since pH is usually more readily controlled than the other variables. Thus, to minimize both hydrogen penetration and hazards of solid salts depositing in normal refinery gas recovery systems, an upper limit of pH 8.3 is highly advisable, since above this maximum pH, deposition of solid salts within tubes or lines readily occurs. When the pH is maintained within the critical range of 7.8 to 8.3, substantially no deposition of ammonium bicarbonate or other solid salts occurs and the rate of hydrogen penctration is held to a minimum.

A third reason for maintaining the pH within the recited critical range is due to the rate of reaction of air with hydrogen sulfide to form sulfur, which in turn reacts with sulfide ions to form polysulfides. Experiments have shown that the oxidation of the sulfide ion to elementary sulfur and the consequent formation of polysulfide is a relatively slow process. On the other hand, the ionic reaction between polysulfide and cyanide (when present) in solution is rapid and complete. The rate of reaction between sulfide and oxygen increases with pH so that in the pH range of 7.8 to 8.3 satisfactory control of hydrogen penetration is obtained with air injection. In in arrows stances where unusually large quantitie s of cyapide. are

produced or where the residence time ot jair in t stream is low, it is possible that the rate qrro polysulfide may be insuflicient to preven yd tration in the equipment. The correct'proeedur'e inthis case is to aerate some of the sour water available from the process and recycle it'tdthe'syste'fia's wasli'water'inl addition to air injection. The use of both polysullide cyanide conte tan rapidly taining hydrogensulfide: The additional damagecaused by the presence of hydrogen cyanid is especially prevaxa nsjqperar.

lent in streams derived from petrol tions. However,hydrogen' blistering is also'associa'ted with such processes as the pumping operation of crude oil fr m. sour crude; il; we ls :Mereimsmker. d d t e walls ottthevcasiuaare subjectsto. hydrogen, t ekrp pe ine trans ortation. iofi soun-ctu er ourl gas rec very pl'ants; andurefinery. gas plants operating, oncomtstraight. run .gas fromcrude .unitsl.

The requirement for; ammoniumlpolysulfidei (or :other water-soluble.. polysulfide) will vary,; o'f vcourse,.- w-ith 1 the precise; constituentspresent in any given system. For example,-if cyanideiepresent',polystglfidezionslreact therewithhto. form thiocyanate. Moreover; ferroustsulfideere? acts withpolysulfide, alsoreducing thetconcentration of thelatter. Consequently, it willtbe realizedtthat the-ex pression of the. present invention cannot .beiba'sedmpon the introduction of a precise amount l'bf polysulfide, but rather must be contemplated in? terms of maintaining; a minimum level; of undestroyecl polysulfi'deuions'; {suchth'at hydrogen-blistering is depressed toia minimumlevel. It: is 'n ecessar-y in the present invention to maintain the aqueous phase in an alkaline-condition, sinceaciddest'roy's polysulfide.

The exact constitution of polysulfides is unknown and various authorities such as Ephraim regard polysulfides asconstituting sulfide solutions containing dissolved free sulfur. Howevenaccor'difngfto othe au thori t'i Qualitative Analysis), 1940;page""11s;--m9 polysulfide ions are understood to include "a "series of -complex'fions based upon sulfide ion (S=) reacted with sulfur Sifto forrn S2=l This ion in turn may be coor d i ted; additional sulfur ions to form ions of greater complexity all 'ofwhich are regarded as polysulfide'sffT The present invention isibase d iipongjthe utilizatio'n 'of polysulfides which are soluble in water principally' 'com'pri 'ng amv mbnilim pq s d alkali s mia lys lfiil ifiti5 3 51.31 d m? "recla rt thiuml o ys l'fidsi hd. at

soluble alkaline earth metal or. tl1er polyvalent metal polysulfides, such as calcium poly lfi F reasons and convenience, urn polysu odium po svl desareprefe r d D 5 t h r nt difiicnlt es volys n. he..qe .t a aly i i lauta d fi ld. leum ttea stwh eh l i srf ma n fie y e} v ry nsicbmp v nd concentrations of ingredients; it issubstantiallyim ble at t irne slto accurately; analyze thesestreams to det mine he; qu ite mQu t rq r fi e h hmus t et d ed o hey em; o, b tanti y: nh b t; hy osent liste i st Consequently, an alternative'procedure has been (devised whereby it may be easily and .quicklyvdetermined; when thecpolysulfi'de haslbee'n reduced to a value such thathy drogenpenetration is'prone to recommence. This -pro cedure involves the use of an instrument designated herein as the standard hydrogen activity probe which is illustrated in Figure III. 4 This probe consists substantially of a thin walled cylinder l made from a inch scheduleSO seamless carbon steeLPipe (ASTM-A-l06) 9 /2 inches long reamed to 0.313, inch insided iameter and reduced, to 10 365, inch es of its length. A A p ted therein so as to leave Thea plar space is closed off at pi the cylinder by any suitable means, such as by welding 3'." By man er vent 4 through the center rod the annularspace is connected to a pressure gauge 6.

of the equipment. A T 5 withfa,valye,7"is provided for relieving the pressure in the probe whenever necessary. The various portions of the probe should be seected o; that: he. total internah o ume; 1i :P I s aheutt i h cent me e htheamq pherewithin@theequiptn nttis;active yep o oti gi pmic ydrqgen.penetrati ns. suchat m c vdw gen wilLditrTusejhrough-the thin wall iOf1thB, probecylinder, will, combine; tov form; molecular; hydrogen within. the annular. space; and will. buildup .a pressure therein; which willbetregistered. on the. gauge, By .noting.the ratev of increase, in. pressure with, respect; to time, t the. hydrogen activity .of theaatmosphere@withimthei'equipment may: be reasonably accurately determined; lthas beentfound that in-..order. to. protect equipment from hydrogen damage, thet-polysulfide content ofrtheaqueous: phase should be maintained; at: a t level such zthatr the standard '1 hydrogen activityprobet indicates a rate. of'increase in pressureof IBSSz thflllll-bQllt l 'lb. per da y, and-preferably less than about1f0.5.-or@ ev en0.2 lb.'per-day.-

Variations oft-the? above-described standard hydrogen activity .probeimaylbe usedg'but in or er that =the -indi-' cate'd pressure variations should becomparable to those for the specificuprobe described herein, the internal vol umetof-the. probe, the'surface area exposed to the: blister ing- .acti-vity,- the thickness ofthe metal wall through whichsatom'ichydrogenpenetrates and the type of metal shoul dabe alllthe same asin the described standard probe. Various expedients. may beemployedin reducing the requirement for. polysulfide' addition or-formation in these. systems, such as water-washing, which is primarily designedtoremove hydrogen-cyanide. This is disclosed anidearadicals results in the reaction of polysulfide with in .a copending application of Efiinger and Renquist, SerialNo. 223,396, filed April 27', 1951, now abandoned.

The. formationofpolysulfide (or addition of 'preformed polysulfide) in alkaline systems containing cycy-auideto-form thiocyanate-radicals. If thiocyanates are allowed to.-accumulate in water accumulators or separators, it has been found that corrosionproducts, such as ferrous sulfide, iron thiocyanate and the like, are formed which-cause, plugging-of screens and obstruction; of the hydrocarbon fiow from the bottom of columns such ast-absorber columns. This is particularly noticeable in gas. recovery systems connected with petroleum refineries.

Investigation of this adverse phenomenon showed that water accumulating at the bottom of gas absorptioncolumns in a gas recovery unit had a pH in the order of about 5.0. On cooling a sample of the accumulated water from such a column, a crystalline material was.

formed which was identified by X-ray diffraction as ammonium-thiocyanate Thedesign and operation of the column should not be. such as to prevent complete removal of ammonium thiocyanate from the bottom of the absorber column under normal processing conditions. Failure toallow for such removal may. result in corrosion of such equipmentas the low carbon steel valve seats of compressors. Deposits on the valve seats have been found to be ferrous sulfide and iron thiocyanate.,-

Investigation leading to a solution of this problem re sulted in the data contained in thelfollowing table Table 1.Efiect of temperature, concentration of ammonium thiocyanate and the presence of air on carrosion rates in ammonium thiocyanate solution at 1 atmosphere HzS partial pressure-corrosion rates in mils peryear Ammonium Thio eyanate, percent W- Saturated pH Rauge 7.35:.1 8.45:.1 7.43:.1 8.43:.1 5.4=i=.1 V

Temperature,F s5 190 s5 85 160 160 s5 85 195 195 Yes Yes No Yes No Yes No Yes No Yes No Yes 1 1 200 7 1 5 200 4 200 10 20 500 1.000 Iueono 1 1 4 1 1 1 1 1 1 Ammonium hydroxide added to the ammonium thiocyauate solution to produce heso pH's after saturation with hydrogen As this table shows, ammonium thiocyanate can cause high corrosion rates in the presence of air or polysulfide at elevated temperatures in both acid and alkaline solutions. However, if the concentration of ammonium thiocyanate is kept below about 10% by weight based on the aqueous phase and the pH is maintained above 7.8, corrosion rates are extremely low even at temperatures as high as F. Consequently, where conditions exist permitting the accumulation of ammonium thiocyanate and the aqueous phase of gas recovery systems to the point where more than about 10% by weight of ammonium thiocyanate is present, the addition of a sufficient amount of water to the absorber columns in the gas recovery system will reduce the concentration of the thiocyanate to such a point that corrosion no longer takes place.

In accordance with one phase of the present invention it is unnecessary to add pre-formed polysulfide since it has been found possible to form polysulfide ions in situ by the addition of an inorganic oxidizing agent to the system containing hydrogen sulfide in the presence of an aqueous alkaline phase. Under these conditions, a portion at least of the hydrogen sulfide is oxidized to form free sulfur which in turn is dissolved in the alkaline aqueous phase and combines with dissolved sulfide in said phase to form a dissolved polysulfide. The inorganic oxidizing agent is preferably an oxygen-containing gas and may be either oxygen per se, air, or mixtures thereof. Hence, in accordance with one aspect of the invention the operation thereof is readily perceived as one preferably involving the determination of the rate of hydrogen penetration as indicated by the standard hydrogen activity probe and thereafter introducing into the system a calculated amount of oxygen-containing gas, periodically or continuously thereafter adjusting the rate of oxygen (or other oxidizing agent) introduction to form sufficient polysulfide ions for the reduction of hydrogen penetration to a desired low value. The amount of oxidizing agent added should be insufiicient to oxidize all of the HzS, but suflicient to react with all of any cyanide present in the system. The rate of reaction between oxygen and hydrosulfide ions is relatively slow, and in cases where little hydrogen sulfide is present or the gas rate is relatively slow, excess unreacted oxygen can accumulate in stagnant vapor areas. It has been noted that this local excess of oxygen itself can lead to hydrogen penetration. This condition can be eliminated by maintaining in the system an amount of oxygen only slightly in excess of that necessary to react with all of the cyanide present therein, but insufiicient to react with all of the hydrogen sulfide present.

The curves given in Figure 11 illustrate the advantages to be gained by the process of the present invention. The curves in Figure ll constitute data which may be obtained by the treatment of refinery streams containing an aqueous phase having dissolved therein ammonium hydroxide saturated'with hydrogen sulfide at atmospheric pressures. The pH of this aqueous phase is arbitrarily adjusted at about 8.7. Curve A in Figure II indicates the rate at which hydrogen penetration occurs in such a system.

Cfilrve C is similar thereto until after the fourth day at which point 0.1 g. of dissolved sulfur (as ammonium polysulfide) per liter of aqueous phase was introduced. It will be noted that following the introduction of ammonium polysulfide the rate of hydrogen penetration was reduced sharply to a negligible figure for approximately three days. At this point the hydrogen penetration again became relatively rapid and a further 0.1 g. of dissolved sulfur as ammonium polysulfide per liter of aqueous phase was added. It will be found that this further addition reduced the hydrogen penetration to substantially nil, at least for a further week. Curve D indicates the effect of cyanide ions upon the conditions existing in the system of curve A. The original system was modified during the second day by the introduction of 2 g. of dissolved sulfur in the form of ammonium polysulfide per liter of the aqueous phase at which point the rate of hydrogen penetration dropped to substantially O. During this period of inactivity successive portions of cyanide ions were introduced in the form of potassium cyanide in amounts calculated to be insufficient to completely react with the ammonia polysulfide present. During the eighth day a final portion of cyanide was added sulficient to react with all of the ammonium polysulfides which remained. It will be noted that hydrogen penetration immediately became excessive.

The complete protection of a system from hydrogen penetration by the introduction of ammonium polysulfide is indicated by curve B, wherein the original system was modified during the second day by the introduction of 0.25 g. of dissolved sulfur in the form of ammonium polysulfide per liter of the aqueous phase. It will be noted that the proportion of ammonium polysulfide was sufficient to cause substantially perfect inhibition of hydrogen activity for a period of about 2 weeks.

This application is a continuation-in-part of our copending application Serial No. 337,308, filed February 17, 1953, now abandoned.

We claim as our invention:

1. In a process wherein a hydrocarbon product in gaseous state containing hydrogen sulfide and an aqueous phase is contacted in a confined system by a ferruginous metal under conditions which normally result in hydrogen blistering of said metal, the improvement comprising maintaining said aqueous phase at a pH between 7.8 and about 8.3 by the introduction of ammonia, and introducing air into the system whereby hydrogen sulfide is oxidized to produce sulfur, and said sulfur dissolves in the aqueous phase to form soluble polysulfidesin an amount suflicicnt to maintain substantial inhibition of hydrogen blistering of said metal the amount of air introduced beinginsufiicient to oxidize all of the hydrogen sulfide.

2. In a process wherein a hydrocarbon product containing hydrogen sulfide, ammonia and water is contacted in-a confined system by a ferruginous metal under conditions which normally result in hydrogen blistering said metal, the improvement comprising maintaining said waterlat a pH between about 7.8 and about 8.3 by the introduction of ammonia, and introducing an oxygencontaining gas into the system, whereby hydrogen sulfide is oxidized to produce sulfur and said sulfur dissolves in the water and reacts with ammonia and hydrogen sulfide to form ammonium polysulfides' in an amount of between about 0.01% and about 0.5% by weight of the aqueous phase, said polysulfide concentration being maintained to substantially inhibit hydrogen blistering of said metal the amount of air introduced being insufficient to oxidize all of the hydrogen sulfide.

3. In a process wherein a hydrocarbon product containing hydrogen sulfide, ammonia and water is contacted in a confined system by a ferruginous metal under conditions which normally result in hydrogen blistering of said metal, the improvement comprising maintaining said water at a pH between about 7.8 and about 8.3 by the introduction of ammonia, and introducing air into the system, whereby hydrogen sulfide is oxidized to produce sulfur and said sulfur dissolves in the water to form ammonium polysulfides in an amount of between about 0.02 and about 0.1% by weight of the aqueous phase, said polysulfides concentration being maintained to substantially inhibit hydrogen blistering of said metal the amount of air introduced being insufiicient to oxidize all of the hydrogen sulfide.

4. In a process for recovering and separating the efiluent gases from a cracking unit into normally gaseous hydrocarbon products and normally liquid hydrocarbon products of the nature of gasoline, which products contain a hydrogen blistering proportion of hydrogen sulfide and cyanide, the combination of steps of intimately contacting said eifiuent gases with an aqueous solution of a polysulfide in gas recovery vessels and maintaining a concentration of polysulfide between about 0.01% and about 0.5% by weight of the aqueous phase in said vessels, said amount being sutficient to substantially reduce the hydrogen blistering of metals containing the bases, the pH of the aqueous phase of said mixture being simultaneously maintained between 7.8 and 8.3 the polysulfide concentration being maintained by introduction of air in an amount suflicient to convert all of the cyanide ions to thiocyanate ions and insufiicient to oxidize all of the hydrogen sulfide present.

5. In a process wherein a hydrocarbon product containing hydrogen sulfide and an aqueous phase is contacted by a ferruginous metal under conditions which normally result in hydrogen blistering of said metal, the improvement comprising maintaining said aqueous phase at a pH between 7.8 and 8.3 and introducing a minor proportion of oxygen into the system, whereby a portion of the hydrogen sulfide is oxidized to produce sulfur, and said sulfur dissolves in the alkaline aqueous phase containing sulfide to form a polysulfide in an amount sufficient to maintain substantial inhibition of hydrogen blistering of said metal said amount being between about 0.01% and about 0.5% by weight of the aqueous phase, and the amount of oxygen introduced being insufficient to oxidize all of the hydrogen sulfide.

6. A process according to claim 5 wherein the process comprises pumping operations in a crude oil well containing hydrogen sulfide.

7. A process according to claim 5 wherein the process comprises transporting hydrogen sulfide-containing crude oil in a pipeline.

8. A process according to claim 5 wherein the process comprises recovery of straight run refinery gases con taining hydrogen sulfide.

9. In a process wherein a gaseous hydrocarbon product, containing contaminating amounts of an aqueous phase, hydrogen sulfide and a cyanide is confined in a ferruginous metal vessel under conditions which normally result in hydrogen damage thereto, the improvement comprising introducing an oxygen-containing gas into said vessel, whereby part of said sulfide ions are converted to polysulfide ions, the amount of polysllfide formed being sufficient to convert substantially all of said cyanide to thiocyanate, and the amount of air being insufiicient to react with all of said sulfide, the pH of the aqueous phase being maintained between about 7.8 and about 8.3 the amount of oxygen being insutficient to oxidize all of the hydrogen sulfide present in the system. 7

10. A process according to claim 9 wherein the concentration of by-product thiocyanate in the aqueous phase is maintained below about 10% by weight calculated as ammonium thiocyanate.

References Cited in the file of this patent UNITED STATES PATENTS 1,300,816 Cobb Apr. 15, 1919 1,844,475 Morrell et al. Feb. 9, 1932 2,020,661 Schllze et al Nov. 12, 1935 2,034,837 Schulze et al. Mar. 24, 1936 2,499,435 Whitacre Mar. 7, 1950 

1. IN A PROCESS WHEREIN A HYDROCARBON PRODUCT IN GASEOUS STATE CONTAINING HYDROGEN SULFIDE AND AN AQUEOUS PHASE IS CONTACTED IN A CONFINED SYSTEM BY A FERRUGINOUS METAL UNDER CONDITIONS WHICH NORMALLY RESULT IN HYDROGEN BLISTERING OF SAID METAL, THE IMPROVEMENT COMPRISING MAINTAINING SAID AQUEOUS PHASE AT A PH BETWEEN 7.8 AND ABOUT 8.3 BY THE INTRODUCTION OF AMMONIA, AND INTRODUCING AIR INTO THE SYSTEM WHEREBY HYDROGEN SULFIDE IS OXIDIZED TO PRODUCE SULFUR, AND SAID SULFUR DISSOLVES IN THE AQUEOUS PHASE TO FORM SOLUBLE POLYSULIDES IN AN AMOUNT SUFFICIENT TO MAINTAIN SUBSTANTIAL INHIBITION OF HYDROGEN BLISTERING OF SAID METAL THE AMOUNT OF AIR INTRODUCED BEING INSUFFICIENT TO OXIDIZE ALL OF THE HYDROGEN SULFIDE. 